Improper prescribing of medications is an important public health problem. Because the aged are more likely to have concomitant illnesses and medications, they are at greatest risk for adverse outcomes. For example, one study conducted in the elderly found that 28% of hospital admissions were due to medication problems, and showed that Medicaid recipients were at an especially increased risk. Drug utilization review (DUR) is a procedure that seeks to reduce the consequences of improper prescribing. In part because of federal mandate, retrospective DUR is now being applied to millions of older Americans, including all Medicaid enrollees and seventy- five percent of all people with prescription insurance coverage. This is despite the complete absence of rigorous evidence indicating that DUR is effective in either altering drug therapy or improving health outcomes. Given the existing federal mandate, an experimental trial of DUR in the Medicaid population is infeasible. Therefore, a timely, well-controlled observational trial of DUR's effectiveness is badly needed. The University of Pennsylvania has a unique opportunity to conduct a rigorous observational trial of DUR's effects on prescribing patterns and on clinical outcomes. Using a large, unique data source, we intend to evaluate the effects of DUR on both process measures and clinical outcome measures. The methodology that we propose incorporates both pre-post intervention comparisons, and concurrent controls. This will enable us to measure a number of important effects of DUR, controlling for possible effects of differences between state programs and causally unrelated secular trends. We intend to employ three distinct, complementary sampling frames from which to pose the study questions. The study questions have been carefully selected, and address issues of practical and theoretical importance. The results of this study, whether positive or negative, will have wide-ranging health policy and scientific implications, especially with regard to the aged. The University of Pennsylvania has a great deal of experience in pharmaceutical outcomes research projects such as this, especially those using large claims databases. The investigators will be able to provide clear, meaningful answers to the study questions in a very short time-frame, and do so in a very cost-efficient manner.